BLBS102-c13 BLBS102-Simpson March 21, 2012 13:15 Trim: 276mm X 219mm Printer Name: Yet to Come
256 Part 2: Biotechnology and Enzymologymuscle in seafood and of the responses the enzymes show to
various processing parameters, however, is sparse. Extensive
reviews of work done on the lipases and phospholipases in
seafood has been presented by Lopez-Amaya and Marangoni
(2000a,b).ENDOGENOUS ENZYMATIC REACTIONS
DURING THE PROCESSING OF SEAFOODDuring seafood processing such as salting, heating, fermenta-
tion, and freezing, endogenous enzymes can be active and con-
tribute to the sensory characteristics of the final product. Such
endogenous enzyme activities are sometimes necessary in order
to obtain the desired taste and texture.Salting of FishSalting has been used in many countries for centuries as a means
of preserving fish. Today, the primary purpose of salting fish
is no longer only to preserve them. Instead, salting enables
fish products with sensory attributes that are sought after, such
as salted herring and salted cod, as produced on the northern
European continent and in Scandinavia. Enzymatic degradation
of muscle proteins during salting is a factor that contributes to
the development of the right texture and taste of the products.Ripening of Salt-Cured FishSpiced sugar–salted herring in its traditional form is made by
mixing approximately 100 kg of headed, ungutted herring with
15 kg of salt and 7 kg of sugar in barrels, usually adding spices
as well. After a day or two, after a blood brine has been formed,
saturated brine is added, after which the barrels are stored at
0–5◦C for up to a year. During this period, a ripening of the
herring takes place, and it achieves its characteristic taste and
texture (Stefansson et al. 1995). ́
During the ripening period, both intestinal and muscle pro-
teases participate in the degradation of muscle protein, contribut-
ing to the characteristic softening of the fillet and liberating free
amino acids and small peptides that help create the characteris-
tic flavor of the product (Nielsen 1995, Olsen and Sk ̊ara 1997).
Studies have shown that intestinal trypsin- and chymotrypsin-
like enzymes migrate into the fillet, where they play an ac-
tive role in the degradation of muscle proteins during storage
(Engvang and Nielsen 2000, Stef ́ansson et al. 2000). Further-
more, Nielsen (1995) shows that muscle amino peptidases are
also active in the salted herring during storage.
In southern Europe, a similar product based on the use of
whole sardines or anchovies is produced. In contrast to the salted
herring from Scandinavia, these salted sardines and anchovies
are stored at ambient temperature, which can vary between 18◦C
and 30◦C (Nunes et al. 1997). Nunes et al. (1997) found that
proteases from both the intestines and the muscles participated in
the ripening of sardines(Sardina pilchardus).Hernadez-Herrero
et al. (1999) reported an increase in proteinase activity as well
as in protein hydrolysis during the storage of salted anchovies(Engraulis encrasicolus)and found a close relationship between
proteolysis and the development of the sensory characteristics
of the product.Production of Fish Sauce and Fish PasteFish sauce and fish paste are fermented fish products produced
mainly in Southeast Asia, where they are highly appreciated food
flavorings. Fish sauce is the liquefied protein fraction, and fish
paste is the “solid” protein fraction obtained from the prolonged
hydrolysis of heavily salted small pelagic fish. Production takes
place in closed tanks at ambient tropical temperatures during a
period of several months (Gildberg 2001, Saishiti 1994). The
hydrolysis represents the combined action of the fishes’ own
digestive proteases and of enzymes from halotolerant lactic acid
bacteria (Saishiti 1994). Orejani and Liston (1981) concluded,
on the basis of inhibitor studies, that a trypsin-like protease is one
of the enzymes responsible for the hydrolysis. Vo et al. (1984)
detected a high and stable level of activity of intestinal amino
peptidase during the production of fish sauce. Del Rosario and
Maldo (1984) measured the activity of four different proteases in
fish sauce produced from horse mackerel. During a four-month
period of measurement, they found the activity of cathepsins
A, C, and B to be stable and that of cathepsin D to decrease.
Raksakulthai and Haard (1992) found that cathepsin C obtained
from capelin was active in the presence of 20–25% salt, sug-
gesting that this enzyme is involved in the hydrolysis of capelin
fish sauce. These studies indicate that several different proteases
need to be active and that their concerted action is necessary to
achieve the pronounced hydrolysis required for production of
such fish sauces.
It is notable that the similarly high storage temperatures
present in southern Europe do not lead to a solubilization of
salted sardines and anchovies. Ishida et al. (1994) reported that
at 35◦C salted Japanese anchovies(Eriobotrya japonica)de-
graded to a marked degree, whereas at this temperature salted
anchovies from southern Europe(E. encrasicolus)were struc-
turally stable. Also, they detected a thermostable trypsin-like
proteinase in the muscle of both salted Japanese anchovies and
European anchovies, but its activity was much higher in the
Japanese anchovies. An explanation of the difference between
the European and the Asian products might be a large difference
between the hydrolytic enzyme activity of the respective raw
materials.Production of SurimiSurimi is basically a myofibrillar protein concentrate that forms
a gel due to cross-linking of its actomyosin molecules (An et al.
1996). It is made from minced fish flesh obtained mainly from
pelagic white fish of low fat content, such as Alaskan pollack
and Pacific whiting. The mince is washed several times with
water to remove undesired elements such as connective tissue
and lipids. The particulate is then stabilized by cryoprotectants
before being frozen (Park and Morrisey 2000).
Surimi is used as a raw material for the manufacture of various
products, such as imitation crabmeat and shellfish substitutes.